Egg–larval opiine parasitoids (Hym., Braconidae) of tephritid fruit fly pests do not attack the flowerhead-feeder Trupanea dubautiae (Dipt., Tephritidae)

Abstract:  We investigated the potential impact of three opiine tephritid fruit fly parasitoids: Fopius arisanus (Sonan), Fopius caudatus (Szépligeti) and Fopius ceratitivorus Wharton, on the non-target native Hawaiian tephritid, Trupanea dubautiae (Bryan), infesting flowerheads of the endemic Asteraceae shrub Dubautia raillardioides Hillebrand. The three species are the only known opiine fruit fly parasitoids that attack host eggs (but occasionally attack first instars). F. arisanus , which originated in southeast Asia, is now widely established in Hawaii and elsewhere in the world, while the other two are African species currently in quarantine in Hawaii. In the laboratory, field-collected flowerheads of D. raillardioides containing T. dubautiae eggs and first instar larvae were exposed to naïve female wasps of each of the three Fopius species in the absence (no-choice test) or presence (choice test) of papaya fruit infested with eggs of the Mediterranean fruit fly Ceratitis capitata (Wiedemann), the parasitoids' normal host. All three Fopius species visited the papaya fruit much more often than the flowerheads, and displayed normal ovipositional responses (probing and stinging) on the fruit in the choice test. None of the three parasitoid species showed ovipositional responses to flowerheads in either choice or no-choice tests. As a result, not a single T. dubautiae egg or larva was attacked by any of the three parasitoids, indicating that these parasitoids of pest tephritids are unable to recognize the microhabitats of flowerhead-feeding tephritids. The results suggest minimal risk of non-target impact in these biological control agents.     

Factors affecting host selection in an insect host–parasitoid interaction

1. Many parasitoids can develop successfully in different stages of the same host but the costs of parasitism may vary between the stages. The stage of host attacked has generally been determined when there is no choice, giving a misleading impression of host selection or preference.
2. The rate of parasitism by a solitary endoparasitoid, Venturia canescens , of each larval stage of the Indian meal moth, Plodia interpunctella , was examined with and without a host refuge from parasitism. In addition, when given a choice of host stages, with and without a refuge, the influence of parasitoid age on host selection was examined.
3. Wasps were able to parasitize all except the first instar, but second instars experienced significantly reduced parasitism, in both refuge treatments, compared with third to fifth instars. Whilst parasitoid emergence was always significantly less when all host stages had a refuge, the reduction was only marginally significant when second instars were attacked.
4. When given a choice of second- and fifth-instar larvae, wasps consistently parasitized more fifth instars, both with and without a refuge. Moreover, significantly fewer second-instar larvae were parasitized in the presence of fifth instars than when presented alone to the wasps. This pattern of parasitism was unaffected by the increasing age of the parasitoids.
5. Host selection by V. canescens is discussed in terms of host–parasitoid population dynamics and structure.     

Biosteres longicaudatus: Developmental dependence on host (Anastrepha suspensa) physiology

Larvae of Anastrepha suspensa that were in the first day of the third instar were parasitized by females of the solitary endoparasitoid, Biosteres longicaudatus. At the end of the 6-hr oviposition period, larvae were ligated posterior to the ring gland so that some larvae had parasitoids anterior to the ligature while in others, the parasitoids were in the abdomen, posterior to the ligature. Ninety-two percent of the parasitoids anterior to the ligature hatched to the first through third instars. Parasitoids posterior to the ligature had a 75% egg hatch to the first instar only. No larval molts to the second or subsequent instars occurred in these parasitoids. Upon parabiosis to 3-day-old, unparasitized host pupae, the ligated larvae pupated and 97% of the first-instar parasitoids in these parabiosed larval abdomens molted to the second instar. Newly laid parasitoid eggs transplanted to 3-day-old pupal hosts had less than one-third of the egg hatch of those transplanted to first-day third-instar hosts. The data implicate the physiological state of the host (vis-a-vis pupation and associated events) as being an important factor in the development of the endoparasitoid.     

Reproductive biology and small-scale rearing of cherry bark tortrix and its candidate biological control agent

Abstract:  The larval parasitoid, Campoplex dubitator (Hym.,: Ichneumonidae), is under consideration as an agent for classical biological control of cherry bark tortrix (CBT), Enarmonia formosana (Lep.,: Tortricidae), in North America. A comprehensive risk analysis of the candidate agent will require prosperous cultures of both the pest and its parasitoid. We present a rearing method for small-scale production of both species using a bean-based artificial diet, with additional information on the reproductive biology of C. dubitator . Based on estimated survivorship probabilities, a CBT egg had a 70% chance of developing completely to the adult stage under this system. The success of parasitism, however, was very dependent on the instar of the CBT host larva at the time of oviposition. All parasitised first instar larvae died shortly after the attack, rendering them unsuitable for oviposition, while 50% of parasitised second instar larvae died prematurely. In contrast, early mortality was 15–30% for larvae parasitised in the third to fifth instars. Regardless of the instar at oviposition, approximately 90% of the surviving hosts yielded parasitoids, showing a high acceptance by C. dubitator of second to fifth instars for oviposition.     

Regulation of host diapause by an insect parasitoid

Abstract. 1. The interaction between larval development and parasitism by the braconid wasp Cotesia koebelei (Riley), was investigated in a population of the butterfly Euphydryas editha (Boisduval) (Nymphalidae). In this population, the butterfly host has an obligatory overwintering larval diapause.
2. It was found that E. editha larvae harbouring parasitoids were more likely to pass through an extra feeding instar before entering diapause than were non-parasitized conspecifics.
3. In addition, some individuals that were experimentally exposed to multiple parasitoid attacks bypassed diapause completely; these larvae passed through five or six feeding instars, reaching sizes typical of final instar post-diapause larvae.
4. The observed effect of superparasitism occurred regardless of whether the host larvae subsequently produced mature parasitoids, suggesting that parasitoid attack is sufficient to invoke the response.
5. It is proposed that the parasitoid C.koebelei regulates the number of pre-diapause feeding instars of its insect host E. editha, and that some component of the female venom, injected at oviposition, is responsible for this regulation.     

Gregarious development of the solitary endo-parasitoid, Microplitis rufiventris in its habitual host, Spodoptera littoralis

Abstract:  Earlier research has shown that the koinobiont parasitoid, Microplitis rufiventris , attacks and can develop on early instars of Spodoptera littoralis larvae with preference to third instars. However, the present study was carried out using the newly moulted sixth instar larvae at two different temperatures (20 ± 1 and 27 ± 1°C) to study the developmental interaction between the parasitoid and the last instar host larvae. Parasitoid eggs laid in singly parasitized host larvae invariably died. As the number of parasitoid eggs/host larvae increased, the proportion of eggs that hatched and number of viable parasitoid larvae successfully reached to their final instar increased. The effect of superparasitization seems to be dose (no. of eggs + parasitoid factors)-temperature-dependent. The results demonstrate a kind of 'Allee effect' suggesting that superparasitized last instar S. littoralis larvae provide a better host environment than singly parasitized hosts for the parasitoid, M. rufiventris . This may be due to host's hormone and/or low dose of factors injected with parasitoid eggs. The supernumerary individuals of wasp larvae developed normally to the point of emergence but most did not successfully emerge from the host. The improvement of both hatchability and post-embryonic development of parasitoid wasp was significantly (P < 0.01) greater at 20°C than at 27°C. The results of the present study are useful in understanding the evolution of life-history strategies and host range in parasitic hymenoptera.     

Shifting preference between oviposition vs. host-feeding under changing host densities in two aphelinid parasitoids

Destructive host-feeding is common in hymenopteran parasitoids. Such feeding may be restricted to host stages not preferred for oviposition. However, whether this is a fixed strategy or can vary according to resource levels or parasitoid needs is less clear. We tested the trade-off between host feeding and oviposition on two whitefly parasitoids under varying host densities. Females of two aphelinid parasitoids, Eretmocerus hayati and Encarsia sophia were exposed to nine different densities of their whitefly host, Bemisia tabaci, in single-instar tests to identify their functional response. Mixed-instar host choice tests were also conducted by exposing whiteflies at four densities to the parasitoids. We hypothesized that the parasitoid females can detect different host densities, and decide on oviposition vs. host-feeding accordingly. The results showed that both Er. hayati and En. sophia females tended to increase both oviposition and host-feeding with increased host density within a certain range. Oviposition reached a plateau at lower host density than host-feeding in Er. hayati, while En. sophia reached its oviposition plateau at higher densities. At low densities, Er. hayati parasitized most on first and second (the optimal ones), and fed most on third nymphal instars (the suboptimal one) of the whitefly host as theory predicts, while at high densities, both parasitism and host-feeding occurred on first and second instars which are preferred for oviposition. En. sophia parasitized most on third and fourth (the optimal ones), while fed on first instars (the suboptimal one) at low densities, and utilized third and fourth instars for both at high densities. In conclusion, oviposition vs. host-feeding strategy of parasitoid females was found to vary at different host densities. The balance between reserving optimal hosts for oviposition or using them for host-feeding depended on parasitoid life history and the availability of host resources.     

Effects of host instar and size on parasitization efficiency and life history parameters ofOpius dissitus

The braconid parasitoidOpius dissitus Muesebeck (Hymenoptera, Braconidae) produced 1.7 to 3 times more offspring when provided second and third instar leafminers (Liriomyza sativae Blanchard) as compared to first instars. Females arising from parasitization of different instars did not differ significantly in numbers of chorionated eggs in their ovaries at adult eclosion. Development time was prolonged by about two days when parasitoid oviposition occurred in first, as compared to third instar hosts. Parasitoid length was positively correlated with host weight (r²=0.75). Because only 7% of variation in host weight could be explained by host density, parasitoid length varied considerably among hosts reared at the same density. Longevity and lifetime fecundity of parasitoids were inversely related to the weight of their hosts.     

Biology, rearing and field release on Guam of Euplectrus maternus, a parasitoid of the fruit-piercing moth, Eudocima fullonia

The eulophid parasitoid, Euplectrus maternus, is a gregarious ectoparasitoid of the larvae of thefruit-piercing moth, Eudocima (Othreis) fullonia. This parasitoid is indigenous to India and was released into Guam in 1998–99 to aid in the biological control of E. fullonia, an important pest of ripeguava, banana, mango, pomegranate, litchi,papaya, tomato, orange and other fruit crops.In the laboratory, biology and rearing of E. maternus on the larvae of E. fulloniawere studied. In no-choice tests, ovipositionby E. maternus was significantly greateron first and second instar larvae than on thirdinstar larvae. However, in free-choice tests,oviposition by E. maternus wassignificantly greater on second instar larvae,followed by first and third instar larvae. Thisparasitoid did not lay eggs on later instars,either in no-choice or free-choice tests.Females laid a significantly greater number ofeggs (>80%) on the dorsal surface of thelarvae than on either lateral or ventralsurfaces (1 to 8%). In general, more eggs werelaid on abdominal segments 1–3 on larvalinstars one to three. The survival of theimmature stages (from egg to adult) of E. maternus on second instar E. fullonialarvae was 61%, which was significantlygreater than the survival rates on first andthird instar larvae (32% and 26%), indicatingthat second instar host larvae are ideal formass rearing of the parasitoid. Mated femaleE. maternus continuously laid eggs on thesecond instar larvae of E. fullonia forup to 30 days, but the greatest number of eggswere laid during the first week after exposure.When E. maternus laid more than two eggson host larva, more female progeny wereproduced, indicating female-biasedreproduction. Adult parasitoids lived longerwhen fed with a honey: water (50% w/v)solution than with pure honey. Similarly, thefecundity of females increased significantlywhen fed with the honey-water solution whencompared to feeding with pure honey. To date,E. maternus has not established in Guam.     

斑痣悬茧蜂对斜纹夜蛾不同虫龄幼虫的选择及后代发育表现

为探究容性寄生蜂对不同龄期寄主幼虫的选择性及其子代蜂发育表现的关联,通过双选试验观察了斑痣悬茧蜂(Meteorus pulchricornis)对斜纹夜蛾(Spodoptera litura)不同虫龄幼虫的寄生选择,并观察了与子代蜂适合度相关的特性表现.结果表明:斑痣悬茧蜂在4龄与5龄之间未表现出偏好,在2龄和3龄、3龄和4龄之间显著偏好较低虫龄;结茧率在不同寄主虫龄间无显著差异,羽化率随寄主虫龄增大而减小,寄生2、3龄幼虫的子代蜂显著高于寄生5龄;寄生5龄幼虫的子代蜂死亡率比寄生2龄的高2.5倍,比寄生3龄的高5.4倍.寄生3龄幼虫的子代蜂发育历期最短(11.9 d),比寄生4龄幼虫的短6.8 d,比寄生2龄幼虫的短4.7 d;子代蜂体型大小在寄生的寄主虫龄间无显著差异.根据研究结果推测,斑痣悬茧蜂在寄生时可能不是根据寄主龄期来评价寄主品质,而是基于寄主体型大小进行评价.     

Suitability of Bemisia tabaci (Hemiptera: Aleyrodidae) instars for the parasitization by Encarsia bimaculata and Eretmocerus sp. nr. furuhashii (Hymenoptera: Aphelinidae) on glabrous and hirsute host plants

The host instar preferences of Encarsia bimaculata and Eretmocerus sp. nr. furuhashii parasitizing Bemisia tabaci and their development on four host plants, collard, eggplant, cucumber and tomato, were studied in the laboratory. Both of the parasitoids accepted all nymphal stages of B. tabaci, but E. bimaculata preferred third and fourth instars while Er. sp. nr. furuhashii preferred second and third instars under both choice and no choice conditions. Regardless of host stage parasitized, adults of parasitoids emerged only from fourth instars. When given the simultaneous choice of all instars, E. bimaculata reduced parasitization of first and second instars (3.73 and 4.76%, respectively) while increasing parasitization of third and fourth instars (5.44 and 6.93%, respectively), in contrast Er. sp. nr. furuhashii increased its parasitization of second and third instar nymphs (1.27 and 3.17%, respectively) and decreased that of first and fourth instars (7.0 and 3.06%, respectively). Host plants did not significantly influence instar preference for either parasitoid. Developmental periods of both the parasitoids from egg to adult emergence were longest when first instars were parasitized and shortest when fourth instars were selected. Parasitoid developmental time was generally shorter on glabrous plants than on hirsute plants.     

Host Stage Selection and Sex Allocation by Gyranusoidea tebygi (Hymenoptera: Encyrtidae), a Parasitoid of the Mango Mealybug, Rastrococcus invadens (Homoptera: Pseudococcidae)

Host stage selection and sex allocation by Gyranusoidea tebygi Noyes (Hym,, Encyrtidae) were studied in choice and no-choice experiments in the laboratory. The parasitoid reproduced on first, second, and third instars of the mango mealybug, Rastrococcus invadens Williams (Hem., Pseudococcidae), and it avoided hosts that were already parasitized. Host feeding was occasionally observed. Sex ratios of the offspring produced by individual wasps were highly biased in favor of females, whereas the sex ratio of groups of wasps foraging under crowded conditions varied from male biased in smaller hosts to female biased in larger hosts. Females had longer developmental times than males, developed faster in larger mealybugs than in smaller ones, and were always larger than males emerging from the same host instar. Their size increased with the instar of the host at oviposition. About 90% of all ovipositions in second and third instar nymphs resulted from an attack with multiple stings, starting with a sting in the head of the host for the most part. The function of these head stings is either to assess quality of the host or to subdue hosts prior to oviposition. Encounter rates, number of attacks, and number of stings during one attack increased, while ovipositions decreased with host instar. Time investment per oviposition and time spent preening increased with increasing host age because older hosts defended themselves more vigorously than younger ones. Thus, while fitness of the parasitoid increased with host size, fitness returns per time decreased. The implications of this host selection behavior for the biological control of the mango mealybug are discussed.     

斑痣悬茧蜂寄生、发育和生殖特征与寄主幼虫日龄的关系

【目的】“圆屋顶形”假说认为,对单寄生性姬蜂和茧蜂适合度而言,中间龄期幼虫寄主的品质高于更早和更晚龄期幼虫。该假说得到许多研究支持,但这些研究常以寄主幼虫脱皮划分虫龄,很少观测生殖特征,从而难以确切和全面描述适合度随寄主生长发育变化而变化的关系。本研究旨在检验“圆屋顶形”假说。【方法】本研究以斜纹夜蛾Spodoptera litura不同日龄幼虫为寄主,观测斑痣悬茧蜂Meteorus pulchricornis寄生和发育特征,并测定成蜂生殖力。【结果】线性回归分析表明,雌蜂对中间日龄寄主幼虫的寄生率大于对两端日龄寄主幼虫的寄生率;蜂卵至成虫的存活、成虫体型大小及其生殖力（产卵量）等适合度相关特征均表现出中间日龄寄主幼虫处理大于两端日龄幼虫处理。【结论】研究结果支持“圆屋顶形”假说。     

Performance of Microplitis tuberculifer (Hymenoptera: Braconidae) parasitizing Mythimna separata (Lepidoptera: Noctuidae) in different larval instars

The solitary parasitoid Microplitis tuberculifer (Wesmael) is an important biological control agent of various lepidopteran pests in Asia. We examined the preference of M. tuberculifer for different instars of its common host, Mythimna separata (Walker), host instar effects on parasitoid development, and the consequences of parasitism in different stages for growth and consumption of host larvae. The wasp successfully parasitized the first four larval instars of M. separata, but not the fifth, which appeared to be behaviorally resistant. First and second instars were parasitized at higher rates compared to thirds and fourths in no-choice situations, ostensibly due to longer handling times for the latter, but second instars were most preferred in a choice test that presented all stages simultaneously. Although later instar hosts yielded heavier cocoons, the fastest parasitoid development was obtained in second instars. Lower sex ratios were obtained from first instars as females appeared to lay a smaller proportion of fertilized eggs in small hosts. Both weight gain and food consumption of parasitized larvae were reduced significantly within 24 h of parasitism, regardless of the stage parasitized, and final body weights were less than 10% those of unparasitized larvae. Thus, M. tuberculifer has good potential as a biological control agent of M. separata, successfully parasitizing the first four larval instars and dramatically reducing plant consumption by the host in all cases.     

Development of the parasitoid,Cotesia rubecula (Hymenoptera: Braconidae) in Pieris rapae and Pieris brassicae (Lepidoptera: Pieridae): evidence for host regulation

Several recent models examining the developmental strategies of parasitoids attacking hosts which continue feeding and growing after parasitism (=koinobiont parasitoids) assume that host quality is a non-linear function of host size at oviposition. We tested this assumption by comparing the growth and development of males of the solitary koinobiont endoparasitoid, Cotesia rubecula, in first (L1) to third (L3) larval instars of its preferred host, Pieris rapae and in a less preferred host, Pieris brassicae. Beginning 3 days after parasitism, hosts were dissected daily, and both host and parasitoid dry mass was determined. Using data on parasitoid dry mass, we measured the mean relative growth rate of C. rubecula, and compared the trajectories of larval growth of the parasitoid during the larval and pupal stages using non-linear equations. Parasitoids generally survived better, completed development faster, and grew larger in earlier than in later instars of both host species, and adult wasps emerging from P. rapae were significantly larger than wasps emerging from all corresponding instars of P. brassicae. During their early larval stages, parasitoids grew most slowly in L1 P. rapae, whereas in all other host classes of both host species growth to pupation proceeded fairly uniformly. The growth of both host species was markedly reduced after parasitism compared with controls, with the development of P. brassicae arrested at an earlier stage, and at a smaller body mass, than P. rapae. Our results suggest that C. rubecula regulates certain biochemical processes more effectively in P. rapae than in P. brassicae, in accordance with its own nutritional and physiological requirements. Furthermore, we propose that, for parasitoids such as C. rubecula, which do not consume all host tissues prior to pupation, that parasitoid size and host quality may vary independently of host size at oviposition and at larval parasitoid egression.     

Seasonal phenology and stage-specific parasitism of the apple ermine moth, Yponomeuta malinellus Zeller, in Korea

The apple ermine moth, Yponomeuta malinellus Zeller (Lepidoptera: Yponomeutidae), is a tent caterpillar that feeds on Malus spp. in Korea. Populations of the moth in native areas appeared to be regulated by the assemblage of parasitoids. Phenological associations between host stages and parasitoids, susceptible stage(s) of the host for each parasitoid, and stage‐specific parasitism were studied. The egg larval parasitoid Ageniaspis fuscicollis (Dalman) had highest parasitism of first instar larvae (24%), with 14% parasitism of other larval stages. Dolichogenidea delecta (Haliday) was recovered from all larval instars with the highest parasitism rate of second instar larvae (20.1%), followed by 19.9% parasitism of mid‐larval hosts. Herpestomus brunicornis Gravenhorst was reared from second instar larvae through to pupal collection, and had the highest parasitism rate (29.9%) at the pupal stage. The larval pupal parasitoid Zenillia dolosa (Meigen) was recovered from mid‐larval to pupal stages with the highest parasitism rate (5.5%) occurring in third to fourth instar larvae. The host stages for developing A. fuscicollis completely overlap with those of D. delecta, and with those of H. brunicornis to some degree. A statistically significant negative correlation exists between A. fuscicollis and these dominant parasitoids, indicating competitive interaction within the host.     

Diadegma mollipla parasitizing Plutella xylostella: host instar preference and suitability

Oviposition decisions (i.e., host selection and sex allocation) of female parasitoids are expected to correspond with host quality, as their offspring fitness is dependent on the amount and quality of resources provided by a single host. The host size model assumes that host quality is a linear function of host size, with larger hosts believed to contain a greater quantity of resources, and thus be more profitable than smaller hosts. We tested this assertion in the laboratory on a solitary larval–pupal parasitoid Diadegma mollipla (Holmgren) (Hymenoptera: Ichneumonidae) developing on three instars (second–fourth) of one of its hosts, the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). In a no‐choice test, parasitism levels and sex ratio (i.e., proportion of female progeny) were significantly high in hosts attacked in the second instar followed by third then fourth instars. However, the few parasitoids that completed a generation from the fourth instars did so significantly faster than conspecifics that started development in the other two instars. In direct observations, however, the parasitoids (i) randomly attacked the various host instars, (ii) spent a similar period examining the various host instars with their ovipositors, (iii) subdued all three host instars with about the same effort, and (iv) no statistical differences were observed in the attack rates on the three host instars. In a choice test, the females parasitized significantly more third instars followed by second then fourth instars. However, total parasitism in this experiment was 43% lower compared to parasitism of only second instars in the no‐choice test. No significant differences were detected in progeny sex ratios. In both choice and no‐choice tests, significantly more fourth instars died during the course of the experiments than second instars, while third instars were intermediate. The higher parasitism of third than second instars in the choice test indicates that the females perceived larger hosts as higher quality than smaller hosts, despite their lower suitability for larval development.     

Does mother really know best? Oviposition preference reduces reproductive performance in the generalist parasitoid Aphidius ervi

The reproductive success of female parasitoids is dependent on their ability to accurately assess the suitability of a host for larval development. For generalist parasitoids, which utilize a broad range of species and instars as hosts, a set of assessment criteria determines whether a host is accepted or rejected. The suitability of a host, however, can only be imperfectly assessed by the female parasitoid, which can result in the selection of lesser quality hosts for oviposition. In this study we explored the disparity between host quality and host preference using the generalist koinobiotic parasitoid Aphidius ervi Haliday (Hymenoptera: Aphidiidae) and the host Aulacorthum solani (Harris) (Homoptera: Aphididae), the foxglove aphid. The second instar hosts produced the highest level of reproductive success, while third and fourth instars resulted in a substantially reduced reproductive performance. When given a choice of host instars, parasitoids preferred the older hosts for oviposition disregarding their reduced suitability for larval development. Results are discussed in context of mechanisms involved in A. ervi host selection and biases in the criteria used to assess hosts that may arise when parasitoids transfer host species between generations.     

Host-stage selection by Trybliographa rapae, a parasitoid of the cabbage root fly Delia radicum

Host-stage selection by Trybliographa rapae Westwood (Hymenoptera: Figitidae) was studied in choice and no-choice experiments in the laboratory. The parasitoid was able to reproduce in first, second, and third instars of the cabbage root fly, Delia radicum L. (Diptera: Anthomyiidae), but oviposition occurred more frequently in third instars when all three developmental stages were offered simultaneously. Oviposition in third instars increased the rate of development of offspring and their body size, but did not alter sex ratio. Results are discussed in the light of predictions made by the theory of optimal host acceptance.     

Inter- and intra-specific host discrimination in gregarious and solitary endoparasitoid wasps

In nature, most species of Lepidoptera are attacked by parasitoids, and some species may be hosts for several parasitoid species. When hosts are parasitized by more than one female of the same species (=superparasitism) or females of different species (=multiparasitism), then intrinsic competition occurs for control of host resources. To reduce competition, some parasitoids are able to recognize the difference between parasitized and unparasitized hosts. Inter- and intra-specific host discrimination were investigated in the two sympatric species, the gregarious Cotesia kariyai (Watanabe) and solitary Meteorus pulchricornis (Wesmael), endoparasitoids of the Oriental armyworm Mythimna separata (Walker). To measure host discrimination, choice experiments were conducted in which females of both species foraged and chose between healthy host larvae and hosts initially parasitized by either C. kariyai or M. pulchricornis. An olfactory test was also performed to examine the discrimination behavior of the two parasitoids. Our results showed that, in oviposition choice tests, both braconid female wasps were able to discriminate between unparasitized hosts and from four to seven day-old hosts previously attacked by conspecific and heterospecific wasps. On the other hand, superparasitism and multiparasitism occurred even in host larvae that were parasitized two days earlier. However, once the immature parasitoids hosts are at larval stage (1st and 2nd instar), super- and multiparasitism were avoided in the two-choice test, but the latter often occurred in the multiple-choice experiment. Host discrimination abilities may have been based on plant volatile signals incurred from damaged plants and internal mechanisms from four to seven post-parasitized hosts.